It's not really very difficult. If you were sorting roads, you'd just type "road" and add all of the models with "road" in the name into a file along with variations such as "street". This narrows down the number of models left so that you can go through the remaining ones and assign ones that you may have missed such as "rd". Once all of them are sorted, there will probably be a little bit of fine-tuning.
You need to use MTA:SA to preview the models and make sure that the .models files work properly though. Some models have random filenames so you need to preview them. There's a platform with a fence around it that's called "fuuuuuuuuuuck" for some reason.